1. Field of the Invention
The present invention relates to a liquid crystal display device having switching elements such as thin film transistors (hereinafter referred to as "TFTs").
2. Description of the Related Art
FIG. 6 shows an exemplary circuit configuration of a conventional liquid crystal display device having TFTs. A plurality of pixel electrodes 101 are provided on an active matrix substrate (not shown) in a matrix. In FIG. 6, a TFT 102 as a switching element is connected to each pixel electrode 101. A gate electrode of each TFT 102 is connected to a gate line 103. The TFTs 102 are controllably driven by gate signals input to the gate electrodes of the TFTs 102 through the gate lines 103.
A source electrode of each TFT 102 is connected to a source line 104. When the TFTs 102 are driven, data (display) signals are input to the pixel electrodes 101 through the source lines 104 and the TFTs 102. The gate lines 103 and the source lines 104 each run alongside the pixel electrodes 101 so as to substantially orthogonally cross each other.
A drain electrode of each TFT 102 is connected to the pixel electrode 101 and one terminal of a storage capacitor 105. The other terminal of the storage capacitor 105 is connected to a common line 106. Each common line 106 is connected to a common electrode Vcom.
The active matrix substrate having such a configuration is attached to a counter substrate with a liquid crystal layer interposed therebetween. Thus, the liquid crystal display device is produced.
In order to realize color display in such a liquid crystal display device, most typically, color filters are provided on the counter substrate. FIG. 7 is a plan view showing a configuration of a portion in the vicinity of a boundary between two adjoining pixels having color filters of different colors. Herein, it is assumed that color filters 113 are arranged in stripes, the most commonly employed arrangement in a display panel for a lap-top computer or the like.
The color filters 113 which include individual color filters 111 and 112 are formed of a resin having pigments or the like dispersed therein. The color filters 113 have a thickness of about 1 .mu.m. In order to obviate both a lack of a color and a combination of colors, the color filters 111 and 112 need to be provided with an interval d1 therebetween so as not to overlap each other. Although there is variation among the intervals d1 depending on the fabrication process, the interval d1 generally needs to be at least about 5 .mu.m. Moreover, in order to prevent light from leaking through between the filters, an overlap margin d2 needs to be provided so that a black matrix 107 and the color filters 113 provided on the counter substrate overlap each other with certainty. The overlap margin d2 also needs to be at least about 5 .mu.m. Consequently, a line width of the black matrix 107 on the counter substrate needs to be at least (d1+2.times.d2).
Since no voltage is applied to portions of the liquid crystal layer between adjoining pixel electrodes 101, the orientation of liquid crystal molecules in these portions is not controlled. A line 110 needs to be provided on the active matrix substrate with a certain distance from the pixel electrode 101. Therefore, as well as to obviate both the lack of a color and the combination of colors, and in order to block light incident on the portions between the line 110 and the pixel electrode 101, the black matrix 107 needs to be provided on the counter substrate with the line width thereof being at least (d1+2.times.d2).
In other words, the line width of the black matrix 107 needs to be about (d1+2.times.d2) or more regardless of how the color filters 113 are configured. For these reasons, the line width of the black matrix 107 cannot be set smaller than (d1+2.times.d2). Thus, there is a problem that an aperture ratio of the liquid crystal display device cannot be improved to a satisfactory level.